This invention relates generally to a process of joining metal parts and, more particular, relates to vapor phase soldering of aluminum parts.
In the past, metal parts were joined by such methods as dip brazing, soldering, wave soldering, etc.
Waveguide assemblies, for example, some of them quite complicated structurally, can be joined by dip brazing. While this joining method is reasonably satisfactory, there are two disadvantages: the high temperature (1100.degree.F.) can cause physical distortion of the parts; and the flux used in dip brazing is a powerful chemical which removes surface oxide from aluminum so the braze metal can flow. In doing so it attacks all surfaces. This can be detrimental in waveguide interiors since the resulting surface roughness attributes to microwave loss. Residues of brazing flux trapped in corners and crevices are difficult to remove after cooling, and if left there, can lead to corrosion. Some advantages of dip brazing are: parts can be tack welded into position which minimizes fixturing; and all the joints in the assembly are made in one dip operation. But when the apparatus has a high number of joints, etc. then this can become a very time consuming operation. Finally, dip brazing is useful for aluminum parts only whereas the vapor process will work for any metal that accepts solder wetting or which can be electroplated for that purpose.
Another joining method is soldering which is excellent for brass or copper waveguides but when applied to aluminum, the parts have to be electroplated with a metal which will accept solder wetting. Assemblies of multiple parts can be soldered with a torch or a soldering iron as long as care is taken to localize the heat so that previously made joints are not remelted and so that solder does not stay molten long enough to dissolve the electroplated layers.
Wave soldering, an another method, can only be used on one flat surface at a time.
The present invention is directed toward providing a process of joining aluminum parts of a complex structure in which these undesirable characteristics are minimized or removed.